buildsys: gen_bits_syscall_h: do not leave undefined SYS_xxx around

If we end up doing '#undef __NR_xxx', we don't want to leave the
corresponding SYS_xxx symbol defined.  So undef it too.

For example, with the ARM EABI layer, we have a bunch of legacy
syscalls that we define early on and then later undefine (such
as __NR_utime).  But we left SYS_utime defined so code that tests
for that define before using it would be broken (since it'd be
defined to a non-existent symbol).

URL: https://bugs.gentoo.org/425006
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

extra/scripts/gen_bits_syscall_h.sh

@@ -50,7 +50,8 @@ EOF
   sed -n -r -e 's/^UCLIBC(__ARM_NR_|__NR_)([A-Za-z0-9_]*) *(.*)/#undef \1\2\
 #define \1\2 \3\
 #define SYS_\2 \1\2/gp' \
-     -e 's/^UNDEFUCLIBC(__ARM_NR_|__NR_)([A-Za-z0-9_]*).*/#undef \1\2/gp'
+     -e 's/^UNDEFUCLIBC(__ARM_NR_|__NR_)([A-Za-z0-9_]*).*/#undef \1\2\
+#undef SYS_\2/gp'
   cat <<-EOF
 
 #endif